In the design of modern integrated circuits, particularly digital circuits, standard cells having fixed functions are widely used. Standard cells are often pre-designed and stored in standard cell libraries corresponding to various predetermined fabrication processes and/or performance settings. In some applications, a standard cell includes a group of transistors and interconnection structures that provide a Boolean logic function, a storage function, or other predetermined functions. In some embodiments, one or more of the standard cells are logic gate cells. In some embodiments, a standard cell includes AND, OR, NAND, NOR, XOR, INV, AND-OR-Invert (AOI), OR-AND-Invert (OAI), MUX, Flip-flop, BUFF, latch, delay, clock cells, memory cells, or other types of digital or analog cells. At the time an integrated circuit is designed, a layout design of the standard cells is retrieved from the standard cell libraries and placed at desirable locations as a part of an overall layout design of the integrated circuit.